1. Technical Field
The present disclosure relates to a touch screen and, more specifically, to an infrared touch screen gated by touch force.
2. Discussion of the Related Art
Touch screens are touch sensitive display devices that act as both an input device and an output device by incorporating a computer display with a sensory overlay so that information may be displayed and received on the same screen. Touch screens are commonly incorporated into general purpose computers, computer terminals, electronic and computerized appliances, computerized kiosks, personal digital assistants (PDAs), smart phones and other portable electronic devices. Touch screens are particularly suited for devices where portability, simplicity and/or durability are important.
There are a number of different types of touch screen technologies. Resistive touch screens utilize a thin transparent outer layer separated from a thin transparent inner layer by a set of insulating spacers. The outer surface of the inner layer and the inner surface of the outer layer are each coated with a transparent metal oxide coating such as indium tin oxide (ITO). The inner and outer layers thereby function, as a switch. A touch event forces the inner and outer layers into electrical contact thereby completing a circuit. By varying the voltages applied to each layer and by relying on the resistive nature of the ITO coating, the location of the touch event upon the touch screen can be calculated.
However, because resistive touch screens utilize multiple partially transparent layers between the display device and the user, the clarity of the display is compromised. Moreover, with extended use, visual imperfections may occur as the layers degrade thereby creating localized areas of distorted display.
Capacitive touch screens utilize a transparent metal oxide coating such as ITO to provide a continuous electrical current across a sensor having a reference capacitance field. When a person touches an area of the ITO coating either with a finger or a conductive stylus, the reference capacitance field is altered. The change to the capacitance field may be sensed and analyzed to identify the coordinates of the touch event.
However, capacitive touch screens suffer form poor long-term accuracy and other related problems. Moreover, capacitive touch screens may not recognize touches from articles that do not conduct electricity.
Acoustic pulse recognition touch screens utilise multiple piezoelectric transducers to provide an electrical signal from observed vibrations caused by touch. The electrical signals are then compared against known touch profiles to determine the location of the touch event.
Acoustic pulse recognition touch screens are presently quite expensive and as a result are not suitable for common applications.
Infrared touch screens 10, as illustrated in FIGS. 1 and 2, utilize a row of x-axis infrared emitters 16 and a corresponding row of x-axis infrared sensors 18. A column of y-axis infrared emitters 12 and a corresponding column of y-axis infrared sensors 14 are also used. The infrared emitters and sensors 16, 12, 18 & 14 are positioned over the surface of the display device. In the absence of a touch event, all of the infrared sensors 14 & 18 sense infrared light from the corresponding emitters 12 & 16. When a hand 20 or stylus comes into contact with the display device, infrared light emitted from one or more emitters is blocked and this blockage is detected by one or more corresponding sensors that cease to detect infrared light. For example, light emitted from an x-axis emitter 26 is blocked and this blockage is detected by a corresponding x-axis sensor 28 that ceases to detect infrared light. The location of the affected x-axis sensor 28 is then interpreted as the x-axis coordinate of the touch event. Similarly, light emitted from a y-axis emitter 22 is blocked and this blockage is detected by a corresponding y-axis sensor 24 that ceases to detect infrared light. The location of the affected y-axis sensor 24 is then interpreted as the y-axis coordinate of the touch event.
However, infrared touch screens may be susceptible to accidental activation by random objects that may temporarily block the infrared beams such as an insect or dropped napkin, etc.